Action
Configure the TWI (two wire serial interface) when using hardware I2C/TWI.
Syntax
CONFIG TWI = clockspeed
CONFIG TWI1 = clockspeed
Syntax XMEGA
CONFIG TWIC | TWID | TWIE | TWIF = clockspeed
(Config TWI and TWI1 is for ATMEGA and Config TWIX is for ATXMEGA chips)
Syntax XTINY
CONFIG TWI|TWI0 = clockspeed
The XTINY uses TWI0. TWI and TWI0 are similar and can be exchanged.
Remarks
clockspeed |
The desired clock frequency for SCL |
CONFIG TWI will set TWSR pre scaler bits 0 and 1, and TWBR depending on the used $CRYSTAL frequency and the desired SCL clock speed.
Typical you need a speed of 400 KHz. Some devices will work on 100 KHz as well.
When TWI is used in SLAVE mode, you need to have a faster clock speed as the master.
There is no dynamic channel support for I2C
To use the hardware I2C routines and not the Software I2C routines you need to use the $lib "i2c_twi.lbx"! (NOT FOR XMEGA/XTINY)
XMEGA
The XMEGA can contain up to 4 TWI units. When not specifying TWIC, TWID, TWIE or TWIF, the TWIC will be used as the default.
Because the XMEGA can contains multiple TWI busses, a channel identifier MUST be used when addressing TWID,TWIE or TWIF.
This means that your normal I2C code is fully compatible but only with TWIC. Thus omitting the channel identifiers, will automatically use TWIC.
You MUST dimension a variable named TWI_START as a byte. It is used by the xmega TWI library code. Without it, you will get an error.
There are 2 manuals available from ATMEL for every ATXMEGA Chip
| 1. | One Family Manual like for example for a ATXMEGA128A1 it is Atmel AVR XMEGA A Manual |
| 2. | Another Manual for the single chips like for example for an ATXMEGA128A1 it is the ATxmega64A1/128A1/192A1/256A1/384A1 Manual. In this Manual you find for example the Alternate Pin Functions. So you can find which Pin on Port C is the SDA and SCL Pin when you want to use the I2C/TWI Interface of this Port. |
It is important that you specify the proper crystal frequency. Otherwise it will result in a wrong TWI clock frequency.
XTINY
The XTINY can contain up to 1 TWI units.
Because the XTINY can contains multiple TWI busses, a channel identifier MUST be used when addressing TWI1 or up.
This means that your normal I2C code is fully compatible but only with TWI/TWI0. Thus omitting the channel identifiers, will automatically use TWI0.
You MUST dimension a variable named TWI_START as a byte. It is used by the xtiny TWI library code. Without it, you will get an error.
Some processors support multiple TWI interfaces like the MEGA328PB. Use CONFIG TWI1 to configure the second TWI named TWI1. The first TWI which is named TWI0 is referred to as TWI.
See also
$CRYSTAL , OPEN, Using the I2C protocol, I2CINIT
Example using Hardware I2C Pin's over Library: i2c_twi.lbx
'-----------------------------------------------------------------------
' (c) 2016 MCS Electronics
' This demo shows an example of the TWI
' Not all AVR chips have TWI (hardware I2C)
'------------------------------------------------------------------------
'The chip will work in TWI/I2C master mode
'Connected is a PCF8574A 8-bits port extender
$regfile="M8def.dat"' the used chip
$crystal= 4000000 ' frequency used
$baud = 19200 ' baud rate
$hwstack = 40
$swstack = 30
$framesize = 40
$lib "i2c_twi.lbx" ' we do not use software emulated I2C but the TWI
Config Scl = Portc.5 ' we need to provide the SCL pin name
Config Sda = Portc.4 ' we need to provide the SDA pin name
I2cinit ' we need to set the pins in the proper state
'On the Mega8, On the PCF8574A
'scl=PC5 , pin 28 pin 14
'sda=PC4 , pin 27 pin 15
Config Twi = 100000 ' wanted clock frequency when using $lib "i2c_twi.lbx"
'will set TWBR and TWSR
'Twbr = 12 'bit rate register
'Twsr = 0 'pre scaler bits
Dim B As Byte , X As Byte
Print "TWI master"
Do
Incr B ' increase value
I2csend &B01110000 , B ' send the value
Print "Error : " ; Err ' show error status
I2creceive &B01110000 , X ' get a byte
Print X ; " " ; Err ' show error
Waitms 500 ' wait a bit
Loop
End
XMEGA SAMPLE
'----------------------------------------------------------------
' (c) 1995-2021, MCS
' xm128-TWI.bas
' This sample demonstrates the Xmega128A1 TWI
'-----------------------------------------------------------------
$regfile = "xm128a1def.dat"
$crystal = 32000000
$hwstack = 64
$swstack = 40
$framesize = 40
Dim S As String * 20
'first enable the osc of your choice
Config Osc = Enabled , 32mhzosc = Enabled
'configure the systemclock
Config Sysclock = 32mhz , Prescalea = 1 , Prescalebc = 1_1
Dim N As String * 16 , B As Byte
Config Com1 = 19200 , Mode = Asynchroneous , Parity = None , Stopbits = 1 , Databits = 8
Config Input1 = Cr , Echo = Crlf ' CR is used for input, we echo back CR and LF
Open "COM1:" For Binary As #1
' ^^^^ change from COM1-COM8
Print #1 , "Xmega revision:" ; Mcu_revid ' make sure it is 7 or higher !!! lower revs have many flaws
Const Usechannel = 1
Dim B1 As Byte , B2 As Byte
Dim W As Word At B1 Overlay
Open "twic" For Binary As #4 ' or use TWID,TWIE oR TWIF
Config Twic = 100000 'CONFIG TWI will ENABLE the TWI master interface
'you can also use TWIC, TWID, TWIE of TWIF
'!!!!!!!!!!! WITHOUT a channel identifier, TWIC will be used !!!!!!!!!!!!!!
#if Usechannel = 1
I2cinit #4
#else
I2cinit
#endif
Do
I2cstart 'since not # is used, TWIC will be used
Waitms 20
I2cwbyte &H70 ' slave address write
Waitms 20
I2cwbyte &B10101010 ' write command
Waitms 20
I2cwbyte 2
Waitms 20
I2cstop
Print "Error : " ; Err ' show error status
'waitms 50
Print "start"
I2cstart
Print "Error : " ; Err ' show error
I2cwbyte &H71
Print "Error : " ; Err ' show error
I2crbyte B1 , Ack
Print "Error : " ; Err ' show error
I2crbyte B2 , Nack
Print "Error : " ; Err ' show error
I2cstop
Print "received A/D : " ; W ; "-" ; B1 ; "-" ; B2
Waitms 500 'wait a bit
Loop
Dim J As Byte , C As Byte , K As Byte
Dim Twi_start As Byte ' you MUST dim this variable since it is used by the lib
'determine if we have an i2c slave on the bus
For J = 0 To 200 Step 2
Print J
#if Usechannel = 1
I2cstart #4
#else
I2cstart
#endif
I2cwbyte J
If Err = 0 Then ' no errors
Print "FOUND : " ; Hex(j)
'write some value to the pcf8574A
#if Usechannel = 1
I2cwbyte &B1100_0101 , #4
#else
I2cwbyte &B1100_0101
#endif
Print Err
Exit For
End If
#if Usechannel = 1
I2cstop #4
#else
I2cstop
#endif
Next
#if Usechannel = 1
I2cstop #4
#else
I2cstop
#endif
#if Usechannel = 1
I2cstart #4
I2cwbyte &H71 , #4 'read address
I2crbyte J , Ack , #4
Print Bin(j) ; " err:" ; Err
I2crbyte J , Ack , #4
Print Bin(j) ; " err:" ; Err
I2crbyte J , Nack , #4
Print Bin(j) ; " err:" ; Err
I2cstop #4
#else
I2cstart
I2cwbyte &H71 'read address
I2crbyte J , Ack
Print Bin(j) ; " err:" ; Err
I2crbyte J , Ack
Print Bin(j) ; " err:" ; Err
I2crbyte J , Nack
Print Bin(j) ; " err:" ; Err
I2cstop
#endif
'try a transaction
#if Usechannel = 1
I2csend &H70 , 255 , #4 ' all 1
Waitms 1000
I2csend &H70 , 0 , #4 'all 0
#else
I2csend &H70 , 255
Waitms 1000
I2csend &H70 , 0
#endif
Print Err
'read transaction
Dim Var As Byte
Var = &B11111111
#if Usechannel = 1
I2creceive &H70 , Var , 1 , 1 , #4 ' send and receive
Print Bin(var) ; "-" ; Err
I2creceive &H70 , Var , 0 , 1 , #4 ' just receive
Print Bin(var) ; "-" ; Err
#else
I2creceive &H70 , Var , 1 , 1 ' send and receive
Print Bin(var) ; "-" ; Err
I2creceive &H70 , Var , 0 , 1 ' just receive
Print Bin(var) ; "-" ; Err
#endif
End
XTINY SAMPLE
'------------------------------------------------------------------
' (c) 1995-2021 MCS
' xtiny-TWI-scanner.bas
'purpose : scan all i2c addresses to find slave chips
'Micro: tiny816
'------------------------------------------------------------------
$regfile = "atxtiny816.dat" ' the used chip
$crystal = 20000000 ' frequency used
$hwstack = 40
$swstack = 40
$framesize = 40
Config Sysclock = 20mhz , Prescale = 1
Config Com1 = 19200 , Mode = Asynchroneous , Parity = None , Databits = 8 , Stopbits = 1
Waitms 3000 'small delay
Print "XTINY:" ; Hex(rstctrl_rstfr) 'print reset cause
Config Twi0 = 100000 'CONFIG TWI will ENABLE the TWI master interface
I2cinit
Dim Twi_start As Byte , B As Byte
Do
Print "Scan start"
For B = 0 To 254 Step 2 'for all odd addresses
I2cstart 'send start
I2cwbyte B 'send address
If Err = 0 Then 'we got an ack
Print "Slave at : " ; B ; " hex : " ; Hex(b) ; " bin : " ; Bin(b)
End If
I2cstop 'free bus
Next
Print "End Scan"
Waitms 2000 'some delay and then repeat
Loop